Based on the characteristics of Pingdingshan salt field, an equivalent composite unit mathematical model was built to replace the interbedded salt rock. The triaxial creep simulation curve of the model was con-sistent with experimental result of the interbedded salt rock. Meanwhile,three-dimensional numerical simulation of underground cavern was conducted by ABAQUS and the law of creep zone extension and volume reduction under different pressure was discussed. The results show that:(1)The equivalent composite unit has good nu-merical stability at steady-state creep stage. The mudstone interlayer can effectively limit the visco plastic areas and movement of surrounding rock. (2)The composite unit basically presents as small linear deformation under the confining pressure (8 MPa) . The cavern volume shrinkage rate and creep duration showed the lowest val-ues of 3% and 2. 5 respectively. With the increase of internal pressure(8~12 MPa),the equivalent composite unit began to show nonlinear creep deformation. The the volume shrinkage rate reached to a small value (3. 5%) after a short time (2. 5 a). With the rapid decrease of internal pressure(≤4 MPa),the surrounding rock showed nonlinear large deformation with the duration of steady creep and creep rate were increasing. The creep of surrounding rock will occur in next five years. (3) The viscosity coefficient of the plastic zone in the test area is increasing with time,which shows the deformation trend is more and more stable in the process of gas storage. Therefore,store pressure should be controlled in an appropriate range(4~12 MPa) when wheel-ing,particularly the duration of small internal pressure should be reduced.%针对平顶山盐田盐岩层数多、单层厚度薄、泥岩夹层多的特点,建立等效复合单元代替互层状盐岩体,利用ABAQUS软件对马庄井田的地下溶腔进行三维数值模拟研究,探讨不同内压下,腔周塑性区围岩的非线性流变性态以及溶腔体积缩减规律.结果表明:(1)等效复合单元在稳态蠕变阶段具有较好的数值稳定性,泥岩能有效地限制黏塑性区范围以及围岩向洞内位移的发展;(2)在围压(8 MPa)作用下,互层状盐岩单元体基本呈现线性小变形特征,溶腔体积收缩率与蠕变持续时间均呈现最低值,分别为3%与2.5 a,随着内压增大(8~12 MPa),互层状盐岩单元体开始呈现非线性蠕变,但经过较短时间后(2.5 a)体积收缩率逐渐稳定至一较小值,约为3.5%,随着内压的迅速减小(≤4 MPa),腔周盐岩逐渐呈现非线性大变形特征,表现为稳态蠕变时间增长,蠕变速率增加,5 a后围岩蠕变仍在稳定增加;(3)塑性区围岩内的黏滞系数随时间普遍加大,体现了互层状盐岩在储气运行过程中越来越稳定的变形趋势,因此,实际运行时储气压力应控制在合理范围(4~12 MPa),尤其要减少在较小内压下的蓄气运行时间.
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